The present invention relates to ultrasonic imaging with electronic scanning, enabling the exploration of a part or an organ to be analysed, notably in a plan (C scan mode echography) or in depth (B mode echography).
Such an imaging device is capable of numerous applications, particularly in the field of medicine, in which field imaging by ultrasonic offers, over imaging by ionizing radiation (including X-rays), the great advantage of not subjecting the patient to harmful radiation.
Before defining the invention, it would seem desirable to recall some theoretical considerations which relate to the ultrasonic transmitters, although they apply just as well to receivers.
It is possible to design an ultrasonic transducer device whose energy is focused along a line, using a linear array of elementary transducers each of which receives the same signal at ultrasonic frequency, via delay means which delay the signal by appropriate amounts before it is applied to the elementary transducers. The delay means may for instance be delay lines. If the number of signal alternations is high, the need for having one delay line for each elementary transducer may be overcome if it is remembered that the delay may be equal to the 2.pi.-modulo phase for each transducer and if the phase is quantified at some levels within an interval of 2.pi.. A solution is then reached which is of the type used at present in sonar and radar installations and which is quite complex.
There is also known a device for ultrasonic monitoring of tubes (French Pat. No. 1,593,804) which comprises transducers which are successively energized, one at a time, each with a suitable time lag. This arrangement requires the creation of a large number of phase shifts, all different, which leads to an extremely complex system.
A system of submarine ultrasonic monitoring (French Pat. No. 1,569,897) is also known, which is of the "sonar" type comprising a series of elementary transducers positioned symmetrically with respect to a central transducer. On each pair of elementary transducers around the central transducer an electric signal is applied with a particular phase shift or delay. Although this device enables circular scanning to be effected, it does not, on the other hand, provide any focalization.
It is an object of the invention to provide an improved ultrasonic sounding device with electronical translation, which at the same time permits focusing and scanning in a predetermined direction while simple in construction and operation.
There is provided an ultrasonic sounding device comprising an array of N elementary transducers distributed regularly along a line of translation, means for storing the distribution over n successive elementary transducers (n being an integer smaller than N) of the phases corresponding to focusing at a predetermined distance from said line, ultrasonic transmit/receive means and switch means for connecting the individual transducers of any group of n transducers to said transmit/receive means directly and via phase shift means according to the distribution. The phase shift means comprises inverter means causing a phase shift of .pi. and the storing means store the distribution of the transducers connected directly and those connected through the inverter means. The group of the n elemental transducers which are energized is moved at intervals of time along said line. The translation line is generally straight; however, another curve such as a circle may be used.
Such a device is much simpler than those previously known and does not require a phase lag device, but only inverter means to produce binary phase quantization.
Not only a fundamental focusing at distance Y.sub.n is then produced, but also harmonic focusing at the distance .sup.Y n/3, .sup.Y n/5, . . . However, it is sufficient to provide selection with a range gate corresponding to the transit time from the transmitting transducers to the fundamental focusing point and back to the receiver transducer (which may be the same as the transmitting transducers).
The invention will be better understood on reading the description which follows of devices which constitute specific embodiments, given by way of non-limitative examples.